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Scientific
inquiry
Objectives
• Know the definition of science, and its strengths
and limitations.
• Distinguish between hypotheses and theories.
• Explain the impacts of the scientific contributions of
historical and contemporary scientists on scientific
thought and on society.
1. State, in your own words, the definition of science.
Assessment
2. You see an icicle hanging from a branch or roof and notice that the ice
forms in ripples on the surface of the icicle. Which of the following is
a valid way to test a hypothesis about these ripples?
A. Do research for information on the internet.
B. Look for information in textbooks or at a library.
C. Ask a teacher or another knowledgeable person.
D. Do an experiment by creating icicles at different temperatures.
3. Which of the following could be scientific evidence?
a) The speedometer on a car reads 57 miles per hour.
b) A photograph shows the planet Venus at a specific
position in the evening sky.
c) A newspaper headline announces the discovery of a
previously unknown fundamental particle
d) You notice that the temperature outside is 27ºC.
e) A teacher tells you that the atomic mass of carbon is
12.0 grams per mole.
Assessment
4. How did Penzias and Wilson contribute to our understanding of
the origins of the universe?
Assessment
• hypothesis
• theory
• objectivity
• repeatability
• experiment
• scientific method
Physics terms
Science is the study of the physical world.
Science, as defined by the National Academy
of Sciences, is the:
"use of evidence to construct testable
explanations and predictions of natural
phenomena, as well as the knowledge
generated through this process.”
The nature of science
Modern society has a vast and evolving body of
knowledge about the natural world. We
describe this knowledge through models:
•physical models: “The Earth orbits the Sun.”
•mathematical models: “The force of gravity is
given by the following equation . . .”
•conceptual models: “The Sun is surrounded
by a gravitational force field.”
The nature of science
Strengths:
Science is flexible. Scientific knowledge is subject to
constant testing and revision as new knowledge and
new technology becomes available. Changes in science
lead to an ever-increasing understanding of the physical
world.
Limitations:
Science is limited to the study of the physical, testable,
observable world, and is limited to natural explanations
of phenomena.
Science: strengths and limitations
Scientific inquiry
Physics is both a process and a
body of knowledge.
Physics is both a process and a
body of knowledge.
• Knowledge includes facts,
like the mass of an electron.
Scientific inquiry
Physics is both a process and a
body of knowledge.
• Knowledge includes facts,
like the mass of an electron.
• This knowledge is gained
through a skill-based process
known as scientific inquiry.
Scientific inquiry
Scientific inquiry
Scientific inquiry is a process of proposing
and testing potential explanations to
“discover” which ones are true laws of nature.
Scientific inquiry is a process of proposing
and testing potential explanations to
“discover” which ones are true laws of nature.
A scientist might find that when she shines
light on a mirror at an angle θ, the light always
reflects from the mirror at the same angle.
Scientific inquiry
Scientific inquiry is a process of proposing
and testing potential explanations to
“discover” which ones are true laws of nature.
A scientist might find that when she shines
light on a mirror at an angle θ, the light always
reflects from the mirror at the same angle.
If she trys this for different angles and mirrors,
she will discover that it is always true: it is the
law of reflection.
Scientific inquiry
Hypothesis
A hypothesis is a tentative, testable
explanation for observable physical
phenomena.
Hypothesis
A hypothesis is a tentative, testable
explanation for observable physical
phenomena.
Most hypotheses are incomplete or
wrong when first proposed.
A hypothesis is a tentative, testable
explanation for observable physical
phenomena.
Most hypotheses are incomplete or
wrong when first proposed.
Hypotheses are still important because
they provide something that can be
tested and revised.
Hypothesis
A theory is a comprehensive, well-established and
highly reliable explanation of a natural, physical
phenomenon.
Theory
Hypotheses vs. theories
Example:
Newton hypothesized that light is a particle that
bounces off a surface like a billiard ball.
Hypotheses vs. theories
Example:
Newton hypothesized that light is a particle that
bounces off a surface like a billiard ball.
Others proposed that light behaves like a wave.
Example:
Newton hypothesized that light is a particle that
bounces off a surface like a billiard ball.
Others proposed that light behaves like a wave.
Neither hypothesis is completely correct; both were
combined to form a modern quantum theory of light.
Hypotheses vs. theories
Theory vs. hunch
In everyday language you might use the word theory to
describe a hunch that you have about something.
A scientific theory is very different from your hunch.
In everyday language you might use the word theory to
describe a hunch that you have about something.
A scientific theory is very different from your hunch.
•A scientific theory has been tested again and again against
the harshest criticism and always comes up correct.
•The findings have repeatability – other experimenters
who test the theory always observe the same results.
Theory vs. hunch
The scientific method is the process of proposing theories and
rigorously testing them.
A tentative hypothesis becomes a theory only if the outcome of
every single related experiment or observation, made by multiple
researchers, agrees with the hypothesis.
Scientific method
Scientific method
Do these adjectives describe theories, hypotheses, or both?
Test your knowledge
____ a. tentative
____ b. testable
____ c. capable of being observed or supported by
experimental evidence
____ d. well-established
____ e. highly-reliable
____ f. based on natural, physical phenomena
____ g. subject to change
Do these adjectives describe theories, hypotheses, or both?
Test your knowledge
____ a. tentative
____ b. testable
____ c. capable of being observed or supported by
experimental evidence
____ d. well-established
____ e. highly-reliable
____ f. based on natural, physical phenomena
____ g. subject to change
H
B
B
T
T
B
B
Some findings have broad impact
on other scientists and on society.
Each scientist builds on the results of others
and, in the end, deepens our understanding of
the universe.
Let’s look at a few examples.
Impact of scientists
on society
1927:
Georges
Lemaitre
proposes a
Big Bang
theory.
The Big Bang
1927:
Georges
Lemaitre
proposes a
Big Bang
theory.
1948: Alpher and
Herman predict
the universe’s
temperature
based on the
theory.
The Big Bang
1927:
Georges
Lemaitre
proposes a
Big Bang
theory.
1948: Alpher and
Herman predict
the universe’s
temperature
based on the
theory.
The Big Bang
1964: Penzias
and Wilson
verify the
predicted
temperature.
1927:
Georges
Lemaitre
proposes a
Big Bang
theory.
1948: Alpher and
Herman predict
the universe’s
temperature
based on the
theory.
1964: Penzias
and Wilson
verify the
predicted
temperature.
1992: Smoot and
Mather measure
variations in
radiation that led
to present-day
clusters of
galaxies.
The Big Bang
1927:
Georges
Lemaitre
proposes a
Big Bang
theory.
1948: Alpher and
Herman predict
the universe’s
temperature
based on the
theory.
Scientific theories are subject to change as new areas
of science and new technologies are developed.
The Big Bang
1964: Penzias
and Wilson
verify the
predicted
temperature.
1992: Smoot and
Mather measure
variations in
radiation that led
to present-day
clusters of
galaxies.
Near-Earth objects
A geological team found high concentrations
of iridium in rock from the time of dinosaur
extinction.
A geological team found high concentrations
of iridium in rock from the time of dinosaur
extinction.
Only asteroids contain that much iridium.
Theory: dinosaur extinction was
caused by the impact from a giant
asteroid.
Near-Earth objects
Climate change
Many scientists are currently engaged in
research about global temperature changes
and rising sea levels.
Many scientists are currently engaged in
research about global temperature changes
and rising sea levels.
Societal impact:
These findings have led to broad societal
discussions about our impact on Earth’s
climate.
Climate change
In the process of building scientific theories, scientists must
analyze, evaluate and critique scientific explanations.
Tools for analyzing a scientific explanation:
• observational evidence
• logical reasoning
• experimental testing
Scientific analysis
Scientific explanations may be analyzed and
evaluated through observational evidence.
Observational evidence
Example: Observations of the
phases of Venus support the
explanation that both Earth and
Venus orbit the Sun.
The observations of Venus satisfy the
criteria for scientific evidence: they are
objective and repeatable.
Observational evidence
Scientific explanations may be analyzed and
evaluated through observational evidence.
Example: Observations of the
phases of Venus support the
explanation that both Earth and
Venus orbit the Sun.
Scientific explanations may be analyzed
and evaluated through logical reasoning.
Example: The explanation for
the seasons is that Earth’s
rotational axis is tilted about
23°.
Logical reasoning
How does logical reasoning allow
us to analyze this explanation?
If this explanation for the seasons is true
then it logically follows that:
An observer at noontime in
Austin, Texas (30°N latitude)
should see the Sun . . .
•at 53° from vertical in winter.
•at 7° from vertical in summer.
This is exactly what is observed!
Logical reasoning
Scientific explanations may be analyzed and evaluated through
experimental testing.
A well-designed experiment allows you to change one variable to
determine precisely how other variables respond.
Experimental testing
Scientific explanations may be analyzed and evaluated through
experimental testing.
A well-designed experiment allows you to change one variable to
determine precisely how other variables respond.
Experimental evidence must be
carefully critiqued. What are the key
questions a researcher should
consider when evaluating the quality
of experimental results?
Experimental testing
Experimental evidence must be carefully critiqued.
• Is the experiment objective? Are the observations unbiased?
• Could other variables have caused the observed effects?
• Do other researchers observe the same result?
• Has the data been analyzed to understand the uncertainties
in measurement? Are the observed effects greater than the
uncertainties in measurement?
Critiquing experimental results
ALL measured data contains some degree of uncertainty.
This uncertainty, or error, is the unavoidable difference between a
measurement and the true value of the quantity being measured.
But if physics is based on measurement, and all
measurements contain uncertainty, then how can we
ever be confident about scientific explanations based
on experimental evidence?
Uncertainty in measurement
Let’s say a student wants to test this
scientific explanation:
He drops a heavy stone and a light stone
and collects this data on the time to fall.
The student argues that this data
supports his explanation. His friend
says he’s wrong. What is the evidence
for each view? Who is right?
heavy objects fall faster
than light objects.
A test case
Ask yourself:
•What is the observed “effect”?
•What is the uncertainty in the
data? What caused the
uncertainty?
•Is the observed “effect”
significant compared to the
uncertainty in the data?
A test case
• The values for the heavy rock vary
by more than a tenth of a second.
• The average value for the two rocks
differs by only two hundredths of a
second.
A test case
This experiment does not support the
explanation because the experiment
finds no significant difference between
the heavy stone and the lighter stone.
Uncertainty can never be
eliminated.
Taking lots of data allows you
to quantify the uncertainty.
Empirical evidence must
always be evaluated with
respect to uncertainties
before any conclusion can
be made.
Quantifying uncertainty
LogicHow do you know a statement is true?
How is a scientific argument made?
How do you know a statement is true?
How is a scientific argument made?
The if-then structure: If Earth is round then it should be possible to
travel in the same direction and end up back at your starting place.
The if-then argument
How do you know a statement is true?
How is a scientific argument made?
The if-then structure: If Earth is round then it should be possible to
travel in the same direction and end up back at your starting place.
Many steps in scientific inquiry use this kind of reasoning.
The if-then argument
• It is a way to propose potential consequences of a theory being true.
• A proposed consequence is an observable test for the truth of the
theory. If the the consequence is actually observed, the theory is
supported. If the consequence is not observed, the theory is known
to be at least partly incorrect.
Propose an if-then statement involving some aspect of science
that you are familiar with.
Write down your statement.
Discuss your statement with your group.
Try it yourself
Why do things happen?
More logic
We believe the things that occur have causes that may be understood
by humans.
Cause and effect: Objects start to move because unbalanced forces
act on them.
Cause and effect
We believe the things that occur have causes that may be understood
by humans.
Cause and effect: Objects start to move because unbalanced forces
act on them.
Many explanations in science use this kind of structure.
Cause and effect
• The effect is something that happens (things start to move).
• The cause explains why or how something happens the way it does
(an unbalanced force acts).
Identify something that happens in the natural world or in technology.
Write down a statement of cause and effect that outlines at least one
potential cause for the effect you describe.
Discuss your statement with your group.
Try it yourself
1. State, in your own words, the definition of science.
Include the following ideas in your answer: evidence, testable
explanations, predictions, natural phenomena, knowledge
Assessment
1. State, in your own words, the definition of science.
Assessment
Answers will vary but should include ideas found in
the definition:
“Science is the use of evidence to construct testable
explanations and predictions of natural phenomena,
as well as the knowledge generated through this
process.”
2. You see an icicle hanging from a branch or roof and notice that the ice
forms in ripples on the surface of the icicle. Which of the following is
a valid way to test a hypothesis about these ripples?
Assessment
A. Do research for information on the internet.
B. Look for information in textbooks or at a library.
C. Ask a teacher or another knowledgeable person.
D. Do an experiment by creating icicles at different temperatures.
2. You see an icicle hanging from a branch or roof and notice that the ice
forms in ripples on the surface of the icicle. Which of the following is
a valid way to test a hypothesis about these ripples?
Assessment
A. Do research for information on the internet.
B. Look for information in textbooks or at a library.
C. Ask a teacher or another knowledgeable person.
D. Do an experiment by creating icicles at different temperatures.
Assessment
a) The speedometer on a car reads 57 miles per hour.
b) A photograph shows the planet Venus at a specific
position in the evening sky.
c) A newspaper headline announces the discovery of a
previously unknown fundamental particle
d) You notice that the temperature outside is 27ºC.
e) A teacher tells you that the atomic mass of carbon is
12.0 grams per mole.
3. Which of the following could be scientific evidence?
Assessment
a) The speedometer on a car reads 57 miles per hour.
b) A photograph shows the planet Venus at a specific
position in the evening sky.
c) A newspaper headline announces the discovery of a
previously unknown fundamental particle
d) You notice that the temperature outside is 27ºC.
e) A teacher tells you that the atomic mass of carbon is
12.0 grams per mole.
3. Which of the following could be scientific evidence?
Assessment
4. How did Penzias and Wilson contribute to our understanding of the
origins of the universe?
4. How did Penzias and Wilson contribute to our understanding of the
origins of the universe?
Assessment
In 1964, Penzias and Wilson used a microwave antenna to
measure the universe’s temperature. Their findings matched
the temperature predicted by Alpher and Herman in 1948 and
confirmed the Big Bang theory.
